A genealogist and a cop: a great team for uncovering the origins of the crime. On a murder case, genealogist Margot Laurent teams up with Arthur Du Plessis, a young and self-assured cop. Who committed the murder? And why? A murder always has its dark side: a fabricated family history that becomes an urban legend. And who can claim that their family has no secrets? Margot and Arthur strip away the hidden mysteries to shed light on the murder. Arthur is the no-nonsense one, here to arrest the culprit, while Margot, the genealogist, is more interested in the past, in the prehistory of the murder, in what prefigured the tragedy before it happened. Between them, Margot and Arthur bring the events into focus. Here lie hidden family traumas, stories sometimes ignored by those who must endure the aftermath, which give multiple layers to the whodunnit.

A la suite d’une affaire de meurtre survenue dans la région d’Angoulême, le destin de Margot Laurent, généalogiste, croise celui d’Arthur du Plessis, un jeune flic plein d’assurance. Muté de Paris, il doit à contrecœur faire équipe avec cette "civile" de vingt ans son aînée…